Department of Developmental Biology

Head: Ondřej Machoň, MSc, Ph.D.

Department of Developmental Biology focuses on genetic regulation of embryonic development. We use gene conditional knock-out technology in mouse model to reveal specific roles of selected signaling pathways and transcription factors regulating craniofacial, neural, tooth and ear development. Studies in mouse are complemented with experiments in chick and zebrafish embryos. Odontogenesis is also studied in several species of reptiles. Using these experimental organisms we aim to elucidate genetic basis of selected human developmental defects.

Important result in 2016

Population of cells originating in the area giving rise to teeth forms also a part of the oral vestibule externally to teeth

We have shown in this study that the early events in the developing anterior area of the mandible are common to the prospective functional incisor primordia and for the non-dental tissue - the vestibular epithelium, forming the oral vestibule (Fig. 1). Because these cells give rise to teeth, they can keep their odontogenic potential under pathological conditions and become a source of pathologies in non-dental areas externally to dentition, such as peripheral odontomas containing dental tissues or small teeth.

Fig. 1: The development of the oral vestibule with contribution of cells of the early signaling center of mouse incisor. Dissociated epithelium (A) and histological section (B) show the cell population (blue) from the early signaling center of dental epithelium (DE) of the mouse incisor localized not only in the tooth germ of functional incisor (FI) but also in the vestibular epithelium (VE) giving rise to the oral vestibule (VO), development of which is shown schematically (C).

Important result in 2015

Sprouty gene dosage influences temporal-spatial dynamics of primary enamel knot formation.In normal mice, the signalling centres of a premolar rudimentary bud and the first molar anlage fuse together to commonly form one typical signalling centre (primary enamel knot) of the first molar. With decreasing Sprouty2 and Sprouty4 gene dosages, we observed a non-fusion of the above mentioned signalling centres, with consequent formation of a supernumerary tooth primordium from the individually developing premolar bud. Our findings significantly contribute to existing knowledge about supernumerary tooth formation.

Important result in 2014

Three-dimensional analysis of the early development of the dentitionThe present reviews survey data provided by 20 years research of odontogenesis in the laboratory mouse and in humans. Our results disprove the generally accepted concept of dentition morphogenesis, and offer new interpretations of results of studies on interactions between dental epithelium and mesenchyme, and on molecular control of tooth development in the mouse model. Such knowledge is important for future methods aimed to development of tooth biological replacements, when a tooth implant resulting from controlled differentiation of living cells will be anchored to a jaw..

Fig. 1. Summarized data on developing dentition and oral vestibule in human and their tentative comparison with developing teeth in fishes. (A) Embryological textbooks present two parallel U-shaped ridges in human embryos: DL - dental lamina (giving rise to the deciduous dentition) and VL - vestibular lamina or labio-gingival band (where oral vestibule will form). (B) Summarization of our data by 3D reconstructions document no continuous vestibular lamina exists. Instead, a set of discontinuous epithelial structures (ridges and bulges) transiently occurs externally to the dental epithelium. Red - dental epithelium. Yellow or blue – vestibular epithelium. c, m1, m2 – the deciduous canine, first and second molar, respectively. AC – the accessory cap-shaped structure. (D) The schematic pattern of tooth rows (“Zahnreihen”) in fishes. The empty rings and black spots indicate the older and younger teeth, respectively, new teeth are formed at the posterior end of each Zahnreihen. (E) Dental and vestibular epithelium in 8 weeks old human embryonic maxilla in a 3D reconstruction viewed from mesenchymal aspect. Note the reiterative fusions (white asterisks) between the dental epithelium and particular ridges of the vestibular epithelium. c, m1 – the deciduous canine and the first molar, respectively.

Fig. 2. Correlation between Shh signaling centers and developing teeth in the mandible of WT mice. Insert: Shh in situ hybridization of the whole mandible at embryonic day 12.5. Rectangles – functional teeth; round and oval shapes – Shh expression domains of developing teeth. Classical view: According to the literature, Shh expression is present in two signaling centers in each mandible half. The anterior one corresponds to the incisor primordium (I), the posterior one corresponds to the first molar (M1) until embryonic day 14. New view: According to the summary of our recent results, the Shh expression appears in several domains along the antero-posterior jaw axes of the lower jaw. The earlier-appearing domains correspond to the rudimentary tooth primordia in the incisor (pt-green) and cheek (MS-blue; R2-red) regions. Later, the primordia of functional teeth with their signaling centers appear: incisor (I-yellow), first molar (M1-yellow). The signaling centers MS, R2 and M1 appear successively in the distal direction. In adults, the functional M1 takes its origin with the contribution of R2 rudiment (red rectangle). A minor contribution of MS rudiment cannot be excluded (blue rectangle).

Important result in 2013

The Reinterpretation of the data on Shh signaling during the early development of the mouse dentitionThe tooth development in mice is one of the most often used models to study regulation mechanisms of organogenesis. Since recently, this model started to be used to develop methods of tooth engineering and regeneration. Correct interpretation of the morphological and molecular data is an essential prerequisite of the reliable conclusions of developmental studies on the mouse model of odontogenesis.We have shown in our study that the firstly appearing structures and its corresponding Shh expression in the upper incisor region in mice (Fig. 1) are not related to two functional incisors but to the tooth rudiments suppressed during evolution (Hovorakova et al., 2013).

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Fig. 1. The early development in the prospective incisor region in the mouse.(A) Two generations of the Shh expression domains (green and yellow, respectively) and their sequential development are documented on the hybridized upper jaws (B–D), and corresponding 3D reconstructions of the dental and adjacent oral epithelium with visualized Shh expression domains (red), (E–G). Two generations of Shh expression domains correspond to two generations of tooth primordia. The first generation (green arrow) appears anteriorly and it corresponds to the rudimentary primordium. The second generation (yellow arrow) appears posteriorly and it corresponds to the signaling center of the functional incisor.

The upper mouse incisor development study has finished our systematic revision of classical data on mouse model of tooth development published in the most recent paper by Peterkova et al. (2014). We have shown in both the incisor and cheek region of a jaw that the development until ED13 corresponds to the rudimentary tooth primordia suppressed during evolution. This is in contrast to the classical view assuming their correspondence to the functional teeth. However, the primordia of functional teeth appear later (Fig. 2).The developing dentition of mice contains primordia, with progressive or regressive development. The studies on their development allow determination of regulation factors involved in growth stimulation or growth retardation. Such information can be very important for regenerative medicine.